The present invention relates to a magnetic filter for removing cruds in a liquid by filter layers formed by magnetizing filter elements by magnets.
Iron and steel structures such as various vessels and pipes used in nuclear power plants and heat power plants undergo gradual corrosion due to contact with a liquid such as water and corrosion products such as iron oxide particles (Fe.sub.2 O.sub.3, Fe.sub.3 O.sub.4 and so on) (to be referred to as "cruds" in this specification) are produced. As a result, there occurs a phenomenon that the bore of a pipe is gradually clogged or narrowed.
Magnetic filters for instance of the types as shown in FIGS. 1 and 2 have been used to remove such cruds.
FIG. 1 shows a magnetic filter for removing cruds which has been proposed by the same inventor (Japanese Utility Model Application laid open under No. 53210/1983). In this magnetic filter, inner pipes g partially and liquid-tightly extend through a vessel a having an inlet b and an outlet c. The inner pipes g are closed at their upper ends as indicated by h. Filter elements d made of ferromagnetic materials are in the space in the vessel a except the inner pipes g and permanent magnets e are vertically movably inserted into the respective inner pipes g. The inner pipes g are made of non magnetic material while the plugs h closing the upper ends of the inner pipes g are made of a ferromagnetic material. A guide i which is a lower portion of each inner pipe g is made of a ferromagnetic material and is formed integral with the inner pipe g. The filter elements d are packed in the space which is defined around the pipes g by a pair of vertically spaced yoke baffle plates j, in such a way that the movements of the filter elements d are so restricted that they are not permitted to flow through the passage openings of the yoke baffle plates j. Upon energization of a drive device f, the permanent magnets e are displaced in the pipes g above the guides i, so that the filter elements d are magnetized. Under these conditions, a liquid to be treated from a nuclear power plant is charged through the inlet b into the vessel a so that the cruds are attracted by the filter elements d.
In order to remove the cruds attracted by the filter elements d, the drive device f is activated so as to lower the permanent magnets e into the guides i. After the filter elements d have been de magnetized in that manner, cleaning water is charged through the outlet c into the vessel a so as to remove the cruds from the filter elements. The removed cruds are discharged together with the cleaning water through the inlet b out of the vessel a.
In the magnetic filter of the type described above, the layer of filter elements must become dense when magnetized and must be loosened when the cruds are washed. Since the filter elements d are packed only in the spaces between the yoke baffle plates j, there arises the problem that the filtration or cleaning efficiency is low. Furthermore, there is the problem that the direct contact between the permanent magnet e and the ferromagnetic guide i results in contact de magnetization so that the magnetic force is gradually decreased.
FIG. 2 shows another magnetic filter for removing cruds which was also proposed by the same inventor (Japanese Patent Application laid open under No. 96293/1983). This magnetic filter comprises a vessel k through which flows a liquid containing cruds; magnet insertion pipes n which extend liquid tightly downwardly from the top of the vessel k; vertically movable permanent magnets m in the pipes n; a drive device o for vertically moving the permanent magnets m; a filter body p packed with filter elements 1 adapted, when magnetized, to magnetically catch the cruds entrained in the liquid; and a cleaning vessel q for cleaning the filter elements 1 removed out of the filter main body p. The pipe n comprises a pressure resisting guide r and a pressure resisting lower portion s both of which are made of a ferromagnetic stainless steel. When the permanent magnet m is inserted into its lowermost position, the magnetization of the filter elements 1 is effected by the upper and lower magnetic poles.
The filter elements 1 are charged into the vessel k and the drive device o is activated so that the permanent magnet m is inserted into the pressure-resisting portion of the pipe n, whereby the filter elements 1 are magnetized. Under these conditions, a liquid to be treated such as the water from a nuclear power plant is charged into the vessel k so that the cruds are attracted and caught by the filter elements 1 of the filter main body p.
In order to remove the cruds which are attracted and caught by the filter elements 1, the liquid as well as the filter elements 1 are discharged out of the vessel k into the cleaning vessel q. The cruds are removed when the filter elements 1 are cleaned and the filter elements 1 free from the cruds are moved into a hopper u by means of a conveyor t and are charged again into the vessel k.
In the case of the magnetic filter of the type described just above, the filter elements 1 must be packed not only around the permanent magnets m but also into the filter main body p which occupies a substantial volume of the vessel k. As a result, a large quantity of filter elements 1 are required and consequently there arises the problem that the pressure loss is increased during the filtration cycle because of the packed filter elements 1. Furthermore, since the pressure resisting guide r is made of a ferromagnetic material, the contact demagnetization results because of the direct contact of the permanent magnet m with the ferromagnetic component part. As a result, the magnetic force is gradually decreased.
The present invention was made to overcome the above and other problems encountered in the prior art magnetic filters and contemplates to attain the following objects:
(1) to increase the efficiency for attracting and catching cruds by increasing the density of the filter layer when the filter elements are magnetized; PA0 (2) to increase the efficiency for cleaning the filter elements by dispersing and fluidizing the filter elements by decreasing the density of the filter layer when the filter elements are de-magnetized; PA0 (3) to ensure the streamlining action when a liquid to be treated is supplied and to ensure the prevention of the filter elements from being dispersed when they are being cleaned; PA0 (4) to minimize the pressure loss by decreasing the quantity of filter elements; PA0 (5) to ensure the positive de-magnetization of filter elements when they are discharged; and PA0 (6) to increase a useful life of a permanent magnet by preventing the contact de-magnetization caused when the permanent magnet is vertically moved.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of preferred embodiments thereof taken in conjunction with the accompanying drawings.